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Question DetailsAsked on 10/11/2016

Should I replace screened porch carpet with decking? Or can I replace the plywood underneath it to help drainage?

About once a year we get a strong enough rain to soak the carpet. Because the layer underneath is *plywood* the water can pool and the porch can take 3-5 days to dry, depending on temp & sunlight. 3-5 days is easily enough time to encourage mold growth, wood damage, and carpet damage, not to mention preventing use of the porch. The current carpet has to be replaced either way but I also want to solve the drainage problem. Should I...
1) Replace the plywood with decking, hopefully allowing the carpet to dry faster.
2) Never use carpet to begin with (I do really like a screened porch with carpet)
3) Other options...

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Plywood subfloor or decking on a screened-in porch is generally asking for trouble - because even if you have shutters or awning shades or canvas drop shades to keep out rain, there will be occasions where rain comes up unexpectedly (especially if in thunderstorm areas) while you are away from the house.


Historically, common solutions for this have been an awning or lean-to shed type roof extending well out over the screening (plywood, fabric, fiberglass, or full roof) to shield it from mildly blowing rain - but cannot totally stop the infiltration of heavy wind with rain or roof runoff without substantially blocking the view and sun too.


In some such areas the custom is to screen-in the porch well back from the edges of the roof - so there is a covered "veranda" walk on the outer part of porch, then the screen wall, then the "interior" porch space. Of course, this requires a relatively "deep" porch or an addition to porch and roof - takes about a 10 foot deep or deeper porch for this to work.


Some people with sunroom type screened porches that are only used at discrete times keep them closed in with canvas or woven fiberglass curtains or shades on the outside - but that makes the room dark and confined most of the time and can promote vermin infestations and moisture problems. They do make fiberglass screen drape material that can be mounted as a roll-up awning - roll or bunch up with rope controls when in use, lower over screen and corner-tie to eyebolts or such when not in use. These can be opaque or a semi-transparent screen-like material.


Some modern screen porches have a second screen layer - commonly done as a "storm window" unit that is set in place more or less permanently but can be easily removed to clean between the units and clean the screens - the outer fairly fine mesh screen layer is built to catch or at least drastically slow up the water so it runs down or falls between the screens and drains out on the sill to the ground. In windy areas with flying debris issues, the outer screen is coarse to keep out large insects and to handle flying debris, and the inner screen is a fine "transparent" mesh that stops most of the water and lets it drain down to and off the sill.


Some replace the screening with plastic (lucite) panels or full windows, making a few so they can swing open to let air flow through and with bug screening on the "outside" face of that opening - and just have to be sure to close the panels after porch use each time. Again, moisture buildup and mustiness in the deck can occur with this type of closing in (basically making it a sunroom) and heat can build up from solar heating, so ventilation has to be introduced if you do that.


To address your question directly - carpets and screened porches generally don't get along - both from a carpet mildew/mold issue and from it sitting wet on the deck and rotting it - as well as wetting the perimeter walls.


If you replace the plywood with board decking, the carpet will dry out quicker (because of the gaps between deck boards) presuming your area does not have continuous very high humidity after rains, like in the deep south. Of course, the less absorbent and more open space the carpet has the quicker it will dry out - but the contact areas of the carpet with the wood will still be a problem. An open-grid synthetic outdoor carpet or putting green/astroturf type carpet with lots of air spaces in the weave might work - there are ones designed for patio use with lots of air gaps and ridges or nubs on the back to hold it up off the surface it sits on to let air flow through and dry that interface to reduce mildew/mold issues.


If you do decking, I would use a type that moisture does not affect as much - ground-contact rated treated wood (the green-treated copper preservative type, not the orangish Wolmanised) at least (and avoiding direct contact with the perimeter to avoid wet wood rotting the house and any perimeter half-walls). True 100% plastic would probably be better. You can also use treated marine plywood but I would not give that as long a life - probably more around 7-15 years plus or minus rather than 20-30 years for ground-contact rated treated wood (which is only about 3% more expensive for the wood than non-ground contact rated but lasts WAYYYY longer. If decking, note that introduces openings that will cool the deck more than plywood, and also may need screening under the deck to stop insects from getting in - but be sure the screening is put in where it will not trap and build up dirt in contact with the carpet or deck - typically stretched and stapled under the deck joists in a way so it can be removed every 10 years or so if needed to remove lint and dirt. The fiberglass screening works better than wire for this because it can be stretched out as a "cloth" and rolled back up for cleaning - and don't use fine window screening - unless you have severe ant or midge issues or such, you want the coarser flying bug screening which will not build up dirt/dust from above so fast. Of course, if you use a plastic astroturn type carpet/rug, then dirt and lint from above is not such an issue.


One other consideration with deck boards rather than plywood - especially if you use typical 1/4-1/2" spacing - is possible high heel issues on the porch surface,a nd possible high heels punching through the carpet.


Basically, carpet is just not very compatible with your situation unless you use one of the above methods to basically eliminate the blowing-in rain.


You can also try just using throw rugs and try to keep them rolled up by the house wall away fromthe screening when not using the deck and especially when away for several days - and take and hang them up to dry (or have ceiling hooks and one or more removeable rope-hung curtain rod poles on the porch to hang them from to dry after wetting.


Last option - change from screened porch to sunroom where as long as you remember to close the windows rain cannot blow in - but then you need deliberate ventilation measures.


Be sure to keep the porch decking (and carpet) 1/4" or more away from the house - leave an airgap (which could be shielded by a trim piece or flashing) so potentially wet deck wood is not touching the house.. The support joists of course you can't avoid - but there should be ice and water shield between the ledger board and the house and flashing over the top of the ledger board to prevent infiltration of water and dirt there.

Answered 2 years ago by LCD




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